Bluetooth is a wireless communication technology standard for exchanging data between fixed and mobile devices over short distances. In order to use the Bluetooth protocol, a device must be compatible with the subset of Bluetooth profiles (often called services) necessary to use the desired services. A Bluetooth profile is a specification regarding an aspect of Bluetooth-based wireless communication between devices. Two widely used Bluetooth profiles for communication of audio between a Bluetooth source (e.g., smartphone) and a Bluetooth accessory device (e.g., Bluetooth audio headphones) include the Hands Free Profile (HFP) and the Advanced Audio Distribution Profile (A2DP).
The HFP is designed to exchange low latency and relatively lower quality, bi-directional voice audio (e.g., voice data related to phone calls) and has a latency of about 40 milliseconds (ms) but limits the sampling rate either to 8 kiloHertz (kHz) (narrowband, i.e. 4 kHz of audio bandwidth) or 16 kHz (wideband, i.e. 8 kHz of audio bandwidth). Wideband speech HFP packets are encoded using the low-complexity subband codec (mSBC), at a fixed rate of 64 kilobits per second (kbps).
A2DP defines a way to send full bandwidth audio (e.g., higher quality audio such as music) in a single direction, such as from a smart phone to Bluetooth headphones. Most Bluetooth source devices choose a sampling frequency of 44.1 kHz or 48 kHz for A2DP communication. SBC is the mandatory codec used for transmitting A2DP audio and typically sends high quality audio data at around 350 kbps. Optional codecs like Advanced Audio Coding (AAC) usually send audio data at around 250 kbps. A2DP audio is sent over the Logical Link Control and Adaptation Protocol (L2CAP), which schedules packets asynchronously. This gives a source device more flexibility to interleave the higher bandwidth audio data with other radio frequency (RF) (e.g., Bluetooth & WiFi) traffic. However, more jitter is generally involved in the delivery of L2CAP packets and the source device does not guarantee when those packets will be delivered to the target device. Thus, more audio has to be buffered up by the target device before being played to avoid audio dropouts, which, as a result, increases the latency of the audio received at the target device.
Accordingly, methods for communicating high quality audio data over a Bluetooth link at lower link latencies, as well as apparatuses and systems configured to implement these methods are desired.